DE60310381T2 - AL-MG ALLOY BRACKET OR TAPE FOR THE PRODUCTION OF CURVED PARTS WITH SMALL BENDING ADLER - Google Patents

Abstract

The invention relates to an aluminium alloy sheet or strip with a thickness of between 1 and 5 mm which is intended for the production of stamped and bent parts having a small bend radius, the composition ( % by weight) of said alloy comprising: Si<0.4, Fe<0.4, Cu<0.4, Mn + Cr:0.3-0.7, Mg:4-5.5, Zn<1, other elements <0.05 each and <0.15 in total, and the remainder aluminium. Moreover, the inventive sheet or strip presents the following properties: an elastic limit R0.2 in direction T>215 MPa, elongation A80>15 % and a difference Rm - R0,2 >80 MPa. Said sheets and strips are used, for example, for the production of parts for motor vehicles, such as reinforcements for openable panels or jacks.

Description

Territory of invention

The The invention relates to the production of curved and mostly drawn Parts with a small bending radius, especially for the automotive industry made of sheet metal or ribbons Aluminum alloy of aluminum-magnesium type, i. the series 5000 according to the nomenclature of the Aluminum Association.

State of technology

Aluminum-magnesium alloys containing more than 4% magnesium are widely used in the automotive industry for parts other than the body shell, such as reinforcements or structural members, which may be formed by drawing or bending. They provide good mechanical strength and, like the 6000 series skin alloys, do not need to be heat treated by solution annealing and quenching. As examples, the alloys 5019, 5182 and 5083 are mentioned, whose composition registered by the Aluminum Association (% by weight) is given in Table 1: TABLE 1

task

The Production of drawn and bent parts requires a material with sufficient formability to the drawn areas of the parts to be able to realize and with a better bending ability, the smaller the bending radii should be, typically in the order of the thickness of the sheet. This ability must be equally good both in the rolling direction and in the transverse direction be. The sheet or strip must have the highest possible mechanical strength to maximize the thickness and in this way the effect of optimal weight reduction as a result of use of aluminum compared to steel.

moreover be automotive parts when baking the body paintwork a heat treatment subjected to a temperature between 150 and 200 ° C during 15 It takes up to 30 minutes. Consequently, there must be a possible loss at mechanical strength during considered this process be, with this deterioration being as low as possible should. The invention relates to sheets and strips Al-Mg alloy that meets these requirements.

object the invention

The invention relates to a sheet or strip of aluminum alloy of 1 to 5 mm thickness for the production of drawn and bent with a small bending radius parts, with the composition (wt .-%):
Si <0.3 Fe: 0.2-0.4 Mn: 0.3-0.45 Mg: 4.5-5.5 Cr: 0.04-0.1 Cu <0.1 Zn <0, 1, other elements each <0.05 and a total of <0.15, balance aluminum, and in this particular composition R _0.2 in the transverse direction> 240 MPa, A ₈₀ > 15% and R _m -R _0.2 > 90 MPa ,

It also relates to a process for producing such a sheet or strip, comprising casting a rolling ingot of the above composition, hot rolling to a thickness e _c , cold rolling to a final thickness e _{f of} between 70 and 40% of e _c and a recovery anneal a temperature of 180 to 280 ° C without subsequent work hardening.

description the figures

The sole figure represents the results of Example 1 in terms of yield strength R _0.2 and bending radius.

description the invention

The This invention is based on the combination of narrow choice of Al-Mg alloy composition more than 4% Mg and a special manufacturing program in order to the properties to achieve a compromise, in particular between Yield strength, elongation and bendability, the for the production of drawn and bent with a small bending radius Parts particularly favorable is.

at the alloys of the invention These are alloys with more than 4.5% Mg, like the ones above mentioned Alloys 5182, 5019 or 5083. Magnesium contributes to mechanical strength in which the content is adjusted according to the desired strength can be. Above 5.5% Mg leaves pour the alloy heavier and process.

The Control of the total content of manganese and chromium is a crucial one Point for the achievement of all desired Properties. A content below 0.3% improves the elongation, However, it lowers the yield strength without compromising bendability to improve. A content above 0.7% improves the yield strength without excessive reduction stretching, but surprisingly results a bad bend radius.

The method according to the invention for producing the strips comprises casting a rolled bar of the considered alloy, hot rolling to obtain a strip of thickness e _c and its cold rolling to the final thickness e _{f of} between 1 and 5 mm. In order to obtain the desired properties, the final thickness e _f must be 40 to 70% of the hot rolled strip thickness e _c . If the cold rolling degree is not high enough, the desired yield strength can not be achieved. If it is too high, the work hardening coefficient n becomes too low and the moldability is insufficient.

The cold rolled strip is then subjected to a recovery anneal at a temperature of 180 to 280 ° C exposed. The control of this temperature is important: a lack of recovery or too low a temperature is for the strain is harmful. Conversely leads an annealing temperature from above 280 ° C too a recrystallized state with insufficient mechanical Strength.

One essential feature of the process of the invention for the preparation the bands and sheets is the missing one later Work hardening after recovery annealing, either by cold rolling or by band stretching. Such work hardening would indeed increase the yield strength, but to greatly reduce the elongation and strain hardening coefficient, what kind of the formability and bendability unfavorable would. moreover the gain goes to the yield strength during the stoving treatment of the lacquers lost very fast while at the partially solidified and later non-cold-formed products the loss of mechanical strength is lower when baking the paints.

One Another advantage of the lack of work hardening in particular by Band stretching after Teilentfestigung is the recovery of Sheets and strips, which have a low anisotropy, with a difference between the yield strengths in longitudinal and transverse direction of less than 15 MPa and usually less than 10 MPa.

Around a later one Hardening of the metal after Teilentfestigung to Avoid the flatness of the strip during cold rolling and before everything is well controlled during finishing, in particular at longitudinal division relatively narrow and rather thick bands where "saber" deformations too are avoided.

The sheets according to the invention and ribbons are especially good for the production of drawn and bent with a small bending radius Parts especially for the automotive industry. Bend radii are achieved which are smaller at 180 ° than the thickness of the sheet and even less than 80% this thickness are. The work hardening coefficient n is higher than 0.10, causing a rapid increase the mechanical strength of the parts in their shaping and thus contributes to the use of smaller thicknesses.

As examples of use, the reinforcements for intrusion-protected openings are called, the drawn and bent parts and which are subjected to the baking treatment of the paints, in particular the Kataphoreseschichten. In a 20-minute treatment at 200 ° C while the loss of yield strength remains less than 20 MPa. Another interesting use of the sheets and strips according to the invention is the production of jacks, where a significant weight saving compared to jacks made of steel is possible.

Examples

example 1

It Rolling bars were cast from 7 different alloys A to G, wherein the alloys A to E a composition of the invention and the Alloys F and G have a composition not according to the invention. The Compositions (% by weight) are listed in Table 1:

Table 1

The billets were hot rolled to produce 5 mm thick strips and then cold rolled to 3 mm, which is 60% of the thickness of the hot strip. The tapes were then subjected to a recovery anneal at 200 ° C. The yield strength R _0.2 in the longitudinal direction, the elongation at break A ₈₀ according to the standard NF EN 10002-1 was measured by tensile tests on metallic materials and the bending radius at 180 °. The results are given in Table 2:

Table 2

It is noted that the high Mn alloy G has an elongation <15% and a fairly large bend radius which is more than 80% of the thickness. The alloy M with a low Mn content also has a fairly large bending radius. In 1 the compromise between yield strength R _0,2 and bending radius was shown. A radius of 1.5 mm is considered to be acceptable at R _0.2 of 200 MPa and of 2.5 mm at R _0.2 of 280 MPa. The points corresponding to the 5 alloys of the invention, lie to the right of the line and show a good compromise between the two properties. The points corresponding to the alloys F and G lie to the right of the line and consequently do not show an acceptable compromise.

Example 2

A heat treatment at 170 ° C., 185 ° C. or 200 ° C. for 20 minutes was carried out as a simulation of baking treatments of paints of a motor vehicle on sheet metal samples of Example 1 made of Alloy C and E and on a sample of the alloy C, which additionally was work hardened by stretching. The strength properties in the longitudinal direction were measured, ie the breaking strength R _m , the yield strength R _0.2 and the elongation A ₈₀ before and after the heat treatment. The results are shown in Table 3 (for the partially solidified alloy C), 4 (for E) and 5 (for the work-hardened alloy C).

Table 3 (C not work hardened)

Table 4 (E not work-hardened)

Table 5 (C work hardened)

It is found that the drop of R _0.2 due to the heat treatment is much lower in the unconsolidated samples than in the work-hardened sample.

Example 3

On the samples C and E of Example 1, the strength properties R _m , R _0.2 and A _{80 were} measured in the longitudinal direction, at 45 ° and in the transverse direction. The results are given in Table 6:

Table 6

It it is found that the strength properties, in particular the yield strength, depending on the direction of measurement, fluctuate very little.

Example 4

Rolling bars were cast from the alloy of the following composition:

The thickness after hot rolling was changed while the final thickness remained at 3 mm, so that the ratio e _f / e _{c was changed} between 70% and 40%. The final annealing temperature was changed between 200 and 320 ° C. A work hardening after the final annealing was not carried out. In each case, the breaking strength R _m , the yield strength R _0.2 , the elongation A ₈₀ and the work hardening coefficient n were determined. The results, which correspond to an average of 5 measurements, are listed in Table 7:

Table 7

There is a strong decrease of R _m and especially of R _0.2 found when the temperature of the final annealing of 260 to 290 ° C increases, which corresponds to the transition to the recrystallization temperature. In addition, at a given partial debonding temperature, it is found that R _{0.2 increases} at a smaller ratio e _f / e _c , that is, at higher cold rolling, but the elongation and the work hardening coefficient n decrease.

Claims (9)

Aluminum alloy sheet or strip of 1 to 5 mm thickness for the production of drawn and bent with a small bending radius parts, with the composition (wt .-%): Si <0.3 Fe: 0.2-0.4 Mn: 0.3 -0.45 Cr: 0.04-0.1 Mg: 4.5-5.5 Cu <0.1 Zn <0.1, other elements in each case <0.05 and in total <0.15, balance aluminum, characterized in that in the partially solidified state, it has a yield strength R _0.2 in the transverse direction> 240 MPa, an elongation A ₈₀ > 15% and a difference R _m -R _0.2 > 90 MPa. Sheet or strip according to claim 1, characterized in that that its bending radius is smaller at 180 ° as his thickness is. Sheet or strip according to claim 2, characterized that its bending radius is less than 80% of its thickness. Sheet or strip according to one of claims 1 to 3, characterized in that the difference between the yield strength longitudinal and in the transverse direction is less than 15 MPa. Sheet or strip according to claim 4, characterized that the difference between the yield strength in the longitudinal direction and in the transverse direction is less than 10 MPa. Sheet or strip according to one of claims 1 to 5, characterized in that the difference between the yield strength before and after a 20-minute Paint baking at 185 ° C is less than 20 MPa. A method of producing a sheet or strip according to any one of claims 1 to 6, comprising casting a rolling ingot, hot rolling to a thickness e _c , cold rolling to a final thickness of between 70 and 40% of e _c and a recovery annealing at a temperature of 180 up to 280 ° C without subsequent cold deformation. Use of metal sheets or strips according to one of claims 1 to 7 for the production of reinforcements for vehicle openings. Use of metal sheets or strips according to one of claims 1 to 7 for the production of jacks.